2scents –
Last time I checked, it’s a mefurashe halacha in Shulchan Aruch (EH 1:3):
??? ????? ???? ?’ ??? ????? ???? ???? ?”? ????? ???? ???? ??? ????? ???? ???? ????? ????? ?? ???? ????? ???? ?? ??????? ???? ??? ??? ??? ???? ?????? ?????? ?? ????? ???? ??????
And as it says in Yoreh Deah (246:2):
????? ??? ???? ???”? ??? ???
Pretty clear cut.
EH: http://hebrewbooks.org/pdfpager.aspx?req=9727&st=&pgnum=9&hilite=
YD: http://hebrewbooks.org/pdfpager.aspx?req=9147&st=&pgnum=137&hilite=